The present invention relates to a charging device for use in an electrophotographic type copying apparatus, facsimile machine, printer or the like.
Conventionally, a corona charger is employed as the charging device foe use in the electrophotographic type copying apparatus, facsimile machine, printer or the like. In the known corona charges, a wire of 50 to 100 .mu.m in diameter is extended in a metal shield having a mouth portion confronting a photosensitive member so as to be spaced several to 10 mm from a surface of the photosensitive member. A high voltage of 5 to 6 kV is applied to the wire so as to generate an electric charge. The surface potential of the photosensitive member is controlled by providing a grid electrode capable of applying a voltage between the mouth portion and the photosensitive member. In case the known corona charger is employed, a large quantity of ozone is produced, thereby resulting in a deterioration of the photosensitive member and other peripheral members made of rubber or plastics. Meanwhile, the corona charger itself is contaminated by a product produced by generation of ozone and maintenance operations such as cleaning are required to be performed.
Meanwhile, U.S. Pat. No. 4,851,960 discloses a contact type charging method which reduces the quantity of generated ozone. An elastic and electrically conductive roller is depressed against a surface of a photosensitive member and DC voltage or combination of AC voltage and DC voltage is applied to the roller so as to generate a discharge in a minute gap defined between the surface of the photosensitive member and that of the roller in the vicinity of a point of contact therebetween such that the photosensitive member is electrically charged. However, in this method, the surface of the roller is contaminated by toner, etc. which have passed through a cleaning device for the photosensitive member. Thus, a problem arises in that due to a drop of the charging capability of the roller, a blank portion of a copy is dirtied.